Hollow internally cooled turbine blades with liquid, vapor or air as a coolant are sufficiently known. A problem is presented, in particular, by the cooling of the trailing edge region of such blades, through which the coolant flows in closed circuit. The walls forming the trailing edge surround a narrow gap, out of which the heat is to be discharged. For this purpose, for production reasons, the width of the narrow gap should not fall below a minimum value. In order to avoid overheating of the trailing edge, there also should not be any large accumulations of material. Furthermore, for reasons of strength, the wall thickness should not fall short of a specific value. These prerequisites mean that internally cooled blades are provided with large rounding radii at the trailing edge, and this has an adverse effect on the blade efficiency.
A cooling system of the initially mentioned type is known from German Patent No. 32 48 162. The region under consideration is equipped, on its inner walls, with ribs which run parallel to the machine axis from the trailing edge to the web. These ribs are provided for triggering and promoting turbulence. In this case, the ribs are at an appropriate distance from the actual trailing edge which is thus designed to be free of ribs. These ribs have a uniform height along their axial extent. The effective cooling of the actual trailing edge region is effected by blowing out the coolant via appropriately shaped elements.
Further considerations as to how heat transmission in so-called triangular ducts, such as the trailing edge region of a gas turbine blade represents, can be improved by means of ribs are set out in the periodical "Journal of Thermophysics and Heat Transfer", volume 8, No. 3, July-September 1994, on pages 574-579 in an article by Zhang et al.
The problem as regards the triangular ducts equipped with ribs of the same height is, however, that, due to the large cross section at the base of the triangle, too large a quantity of coolant flows through there on account of the low resistance, whereas only a small quantity of fluid, mostly in laminar form, flows in the other vertex of the triangle. This may lead to the inadequacies explained later.